Affected by the recent heavy rainfall, the No. 5 flood of 2020 occurred in the upper reaches of the Yangtze River. During this flood, the upper reaches of the Yangtze River and a total of 62 rivers including the Minjiang, Tuojiang, and Jialing Rivers had over-warning floods. Among them, the Luzhou-Cuntan section of the upper reaches of the Yangtze River and the Minjiang, Tuojiang and Jialing Rivers had over-protection floods. A super-historical flood occurred in the Zhigaochang section. The peak water level of the Gaochang Hydrological Station of the Minjiang Control Station at 21:00 on August 18 was 291.08 meters, which exceeded the guaranteed water level by 3.08 meters. The peak flow at 21:38 was 37,500 m³/second, and the water level and flow were both ranked first since the actual measurement data were available in 1939. (The highest water level in history is 290.12 meters, the highest flow rate in history is 34,100 m³/second, June 1961), the water level fell below the alert at 18:00 on the 19th. At 16:00 on the 18th, the flood peak water level of Fushun Hydrological Station of Tuojiang Control Station was 274.08 meters, which exceeded the guaranteed water level by 0.08 meters. The corresponding flow rate was 10,500 m³/second. The flow rate ranked third since the measured data in 1952 (the historical maximum flow rate was 15200 m³/second. July 1981), at 17:00 on the 19th, the water level fell below the warning level. The flood peak water level of Beibei Hydrological Station of Jialing River Control Station was 200.23 meters at 12:35 on the 19th, which exceeded the guaranteed water level by 1.23 meters, and the corresponding flow was 32,600 m³/second; at 17:00 on the 20th, the water level was 197.46 meters, which was still 2.96 meters above the alarm. The flood peak water level of the Cuntan Hydrological Station at 8:15 on the 20th at 8:15 on the upper reaches of the Yangtze River was 191.62 meters, which exceeded the guaranteed water level by 8.12 meters, ranking second since 1892 (the highest water level in history was 192.78 meters, August 1905), with a maximum flow of 74,600 m³/second; at 17:00 on the 20th, the water level was 191.03 meters, which was still 7.53 meters. It is expected that within 48 hours, the Zhutuo River section of the upper reaches of the Yangtze River, Beibei and Dongjin Tuojiang sections of the lower Jialing River will retreat below the warning water level.
The Three Gorges Reservoir had a maximum inflow of 75,000 cubic meters per second at 8 o'clock on the 20th. It has lasted for 9 hours and is the largest since the establishment of the reservoir in 2003. At 17:00, the water level of the Three Gorges Reservoir was 163.15 meters and the outflow flow was 48,800 cubic meters per second. The water level of the main stream from Yichang, Shashi to Lianhuatang and Dongting Lake below the Three Gorges Reservoir of the Yangtze River exceeds the alarm by 0.07 to 0.69 meters.
The Ministry of Water Resources attaches great importance to flood prevention in the upper reaches of the Yangtze River. E Jingping, deputy commander-in-chief of the State Administration of Defense and Minister of Water Resources, called for strengthening monitoring, forecasting and early warning, scientifically dispatching the reservoirs on the upper reaches of the Yangtze River with the Three Gorges Reservoir as the core, coordinating the safety of flood control in the reservoir area and downstream, and maximizing the benefits of flood prevention and disaster reduction. Ye Jianchun, deputy minister of the Ministry of Water Resources, presided over a conference to analyze and judge the rain and water regimes in the upper reaches of the Yangtze River, and to study and deploy the joint operation of the Three Gorges Reservoir and the upstream reservoir group. The Ministry of Water Resources upgraded the flood and drought disaster prevention emergency response to Level II at 9 o'clock on the 19th, and issued a timely notice to Chongqing City, requesting that the reservoir area be investigated and personnel transferred to avoid danger, and a working group was sent to Chongqing City to assist in guiding the mainstream of the Yangtze River. Flood defense work along the line and the Three Gorges reservoir area. The Yangtze River Water Conservancy Commission of the Ministry of Water Resources initiated the second-level emergency response to flood and drought disaster prevention, and issued 12 dispatch orders. On the 18th, the Three Gorges Reservoir was dispatched twice to increase the discharge flow to 46,000 cubic meters per second and 48,000 cubic meters per second to reduce the reservoir. In addition, the Three Gorges Reservoir’s maximum discharge flow is 49,400 cubic meters per second, and the peak cut rate is 34.1%. At the same time, further excavation of the Yalong River Jinping Class I and Ertan, Jinsha River Xiluodu, Xiangjiaba, The potential of cascade reservoirs in the basins of Wudongde and other river basins has made every effort to intercept floods and reduce the pressure on flood control in the areas along the Yangtze River in Sichuan and Chongqing. According to statistics, from August 16 to 12:00 on August 20, the reservoirs in the upper reaches of the Yangtze River blocked more than 8 billion cubic meters of floodwater, of which the Three Gorges Reservoir blocked about 4 billion cubic meters of floodwater.
The Chongqing Water Conservancy Bureau launched the first-level emergency response for flood control, and rolled out 43 issues of important water regime reports, and successively sent 16 expert groups to key flood control areas to strengthen technical support, and delineated the affected area according to the flood frequency; Tongnan, Jiangjin, Banan and other districts and counties actively responded and safely transferred about 250,000 people in the threatened area, without any casualties. The Sichuan Provincial Water Resources Department initiated the first-level emergency response for flood control, scientifically dispatched key water conservancy projects, maximized the role of flood arrest and peak reduction, and reduced downstream flood control pressure. It dispatched the Minjiang Zipingpu, Pubugou, and Wawushan reservoirs to intercept 600 million cubic meters of floodwater. Reduce the flood peak of Wutong Bridge from once in 100 years to once in 30 years; dispatch the Fujiang Wudu Reservoir to hold 200 million cubic meters of flood, and reduce the flood peak in Mianyang City from 100 years to once in 50 years; dispatch Jialing River Pavilion and Baozhu Temple, Shengzhong Reservoir blocked 1.2 billion cubic meters of flood water, reducing the flood peak from Cangxi to Nanchong from once in 20-30 years to once in 5 years.